In the prior art, there has been developed a process generally referred to as an additive manufacturing process which generally consists of forming and extruding a bead of molten thermoplastic material, applying such bead of molten material in a strata of layers to form a facsimile of an article and then machining such facsimile to provide an end product. Typically, such thermoplastic material is infused with a type of reinforcing fiber to enhance its strength. As a general practice, the molten bead, while still hot and pliable, is tamped down using an oscillating plate to create a flattened layer of material of a specific desired thickness. This process is repeated so that each layer is deposited upon an existing layer to build up a structure. When executed properly, the new material being deposited is of a temperature sufficient enough to allow it to melt and fuse with material previously deposited, thus producing a solid part. The tamping plate is generally configured as a flat plate with a center through-hole, situated concentric with the centerline of the extrusion nozzle, thus providing for effective tamping of the extruded material, regardless of the direction in which the head is moving. This tamping plate not only tamps and flattens the thermoplastic bead but also helps fuse it with the previously laid layer of material.
In the practice of the aforementioned process, several disadvantages have been encountered; most notably, air pockets, which are trapped between layers of thermoplastic material during the extrusion/deposition process, are simply tamped into the structure. In addition to creating problems during any temperature cycling that might occur after the part has cooled and hardened, such entrained air pockets invariably result in internal voids as well as surface imperfections in the final machined article. A further disadvantage of using a tamping plate is the insufficient integration of reinforcing fibers between layers. When two smooth beads of this material are forced together, the plastic component of the bead tends to fuse with the plastic component of the mating bead, with little or no reinforcing fibers crossing the area where the layers meet. Consequently, the joints between layers where there is no reinforcing material seriously affect the structural integrity of the overall article. Additionally, the mechanism employed to quickly oscillate the tamping plate is by necessity, quite complex, expensive and difficult to maintain.
In view of the forgoing, it is the principal object of the present invention to provide an improved method of producing articles through the use of an additive manufacturing process. Another object of the invention is to provide such a machine and method functional to provide more effective fusion of engaging plies of molten material. A still further objective of the invention is to provide such improved machine and method without the requirement of complex and expensive devices.